1. Field of the Invention
The present invention relates to a reflecting mirror which reflects light, and more preferably, relates to a reflecting mirror which is suitable as a door mirror and a fender mirror or the like provided outside of a vehicle.
2. Description of the Related Art
A reflecting mirror being referred to as a so-called door mirror for confirming rearward right and left (may be referred to as an outer view mirror) is provided to a vehicle. In the reflecting mirror, recently, a photocatalytic hydrophilic film consisting of a layer made of silicon dioxide (SiO2) and a layer made of titanium dioxide (TiO2) is formed on a glass substrate (see Japanese Patent Application Laid-Open (JP-A) No. 2000-239047 as one example of the photocatalytic hydrophilic film).
That is, since the reflecting mirror of this type is provided outside the vehicle, the reflecting mirror is exposed to rain in the rain. At that time, the adhesion of water droplet such as rain drop to the surface of the reflecting mirror distorts the reflected image. Therefore, a hydrophilic layer made of silicon dioxide or the like is formed on the surface of the reflecting mirror, and thereby the hydrophilicity of the reflecting mirror is improved. Also, the distortion of the reflected image due to the adhesion of the water droplet is restrained by thinning the water adhering to the surface, or the water droplet is evaporated at an early stage.
On the other hand, in the reflecting mirror of this type, the component or the like (mainly organic substances) of the vehicle emission of other vehicles may adhere to the surface of the reflecting mirror in fine weather, and the surface thereof may be dirty. The dirt on the surface of the reflecting mirror reduces the hydrophilicity of the hydrophilic layer. It is thought that a hydrophilic layer made of silicon dioxide and a photocatalyst layer made of titanium dioxide or the like formed on the side of the glass surface or the opposite side thereof are provided, and organic substances adhering to the hydrophilic layer is decomposed near the surface of the reflecting mirror by the photocatalyst function of titanium dioxide or the like to maintain the hydrophilicity of the surface of the hydrophilic layer.
In the conventional photocatalytic hydrophilic film consisting of the layer of silicon dioxide and the layer of titanium dioxide, the film thickness of the layer of titanium dioxide which has comparatively large refractive index is 150 nm to 300 nm (preferably 500 nm in the structure disclosed in JP-A No. 2000-239047). In contrast, the film thickness of the layer of silicon dioxide which has comparatively small refractive index is 10 nm to 30 nm (0.1 nm to 50 nm in the structure disclosed in JP-A No. 2000-239047), and is thinner than that of the layer of titanium dioxide.
When the photocatalytic hydrophilic film whose the thickness of the layer of titanium dioxide having high refractive index is comparatively thick is formed, comparatively strong surface reflection is generated on the surface of the photocatalytic hydrophilic film by optical interference effect. A problem exists in that the reflected image formed by the surface reflection light on the photocatalytic hydrophilic film and the reflected light on the reflecting mirror is a so-called double image.
Especially, in a recent reflecting mirror for a door mirror, an electrochromic element is formed between a glass substrate and a reflecting film, and the light transmittance of an electrochromic element is reduced. Therefore, the light entering the reflecting film is reduced, and the reflected light is reduced when the light caused by the headlight of the following vehicle is reflected by the reflecting film, thereby improving antidazzle.
A problem is generated in that the double image becomes remarkable by reducing the light transmittance in the reflecting mirror which can reduce the light transmittance if necessary by using the electrochromic element or the like.